Liquid-liquid extraction



US. Cl. 23-269 3 Claims ABSTRACT OF THE DISCLOSURE A liquid-liquid extractor consists of a number of annular cells rotatable about a common vertical axis, so that two immiscible liquids rotated therein form inner and outer annular layers. Each cell has associated with it a U-shaped pipe fixed upon a vertical spindle parallel to and offset from the vertical axis of the cells. Rotation of the spindle causes the pipes to enter the respective cells and so scoop in the inner layers of liquid, each portion of the inner layer flowing along the U-shaped pipe to the next lower cell. The cells are arranged so that each can still hold its contents when rotation ceases and the apparatus is at rest.

This invention relates to liquid-liquid extraction and concerns, in particular, improvements in apparatus for use in carrying out extraction processes using immiscible liquids.

Until recently, known steady-state distribution machines have been complex, delicate and expensive pieces of equipment constructed as a series of settling cells which can be mechanically shaken and associated with lateral transfer units arranged so that, after a shaking and settling cycle, the quantities of one of the immiscible liquids are each transferred to the next cells in one direction and the quantities of the other of the immiscible liquids are each transferred in the opposite direction or, in some machines, one of these two transfers takes place.

A considerable advance in machine construction is provided by the invention disclosed in British Patent No. 998,646, which is based upon the use of a continuously rotating annular cell, in which settling takes place under centrifugal force. This enables many improvements in construction and operation to be provided.

The various preferred embodiments of the improved apparatus shown and described in British Patent No. 998,646 have outer and inner rotary assemblies arranged so as to rotate about horizontal axes and transfer of the liquids after each separation step therefore takes place laterally, which is analogous to the earlier types of shaker/settler machines. It is an object of this invention to provide improved apparatus and, particularly, to make use of the advantages to be gained by arranging the apparatus about a vertical axis.

According to the present invention, therefore, a liquidliquid extraction apparatus includes at least one annular cell arranged to undergo rotation about a vertical axis so as to effect centrifugal separation of liquids therein in the form of layers against the outer part of the cell, the lower part of the cell being arranged to contain the liquid charge for the cell when the apparatu is at rest, and scoop means for collecting one of the layers from the cell being arranged to enter such cell by movement of its inlet end in a plane normal to the vertical axis.

Preferably, the scoop means comprises a cranked pipe associated with two consecutive cells arranged to transfer liquid collected from the upper one of such cells directly and under gravity to the lower cell.

United States Patent One advantage of this arrangement is that the apparatus'can occupy a smaller floor or bench space than a horizontally-arranged unit of similar capacity.

In order that the invention may be readily understood, preferred embodiments are shown by way of example in the accompanying drawing, in which:

FIGURE 1 shows a diagrammatic and fragmentary vertical section of one form of apparatus.

FIGURE 2 shows an alternative form of outer assembly.

Referring to FIG 1, the outer tube which is divided by internal annular divisions to form a plurality of cells is shown at 10. This is arranged to rotate about a vertical axis 11, for instance in the direction of the arrow 12. The partitions provided inside the tube 10 consist of equally-spaced annular plates or rings 13 and contrast with those shown for instance at 11 in FIGURE 9 of the drawings of British Patent No. 998,646 in that short upstanding rims 14, which may be inwardly coned, if desired, are provided on the inner edges of the rings 13.

This arrangement of the tube 10 requires the use of a transfer unit assembly so arranged that the inlet ends of the collector pipes move into the corresponding cells, i.e., move between adjacent rings 13 and, necessarily above the rims 14, in a plane which is normal to the axis 11. This can be conveniently achieved by mounting the transfer units for rotation about a vertical axis 15, for instance in the direction shown by the arrow 16, the axis 15 being offset relative to the tube axis 11. The assembly consists of an upright spindle 17 driven in a manner not shown, for instance through suitable gearing or belt drives from the motor which also drives the tube 10, and carrying a plurality of lateral arms 18. Each arm 18 supports a cranked pipe comprising a collector leg 19 and a discharge leg 20 and arranged so that the legs 19 and 20, in rotating about the axis 15, pass respectively above and below one of the rings 13. As this occurs, the inner layer of liquid is collected by the leg 19 and directed by the leg 20 into the next lower cell, i.e., under gravity. The shaded area 21 and the dotted area 22 indicate the positions of the outer and inner layers as they are formed during the settling phase; the outer shaded area 23 indicates the position of the residual layer when the apparatus is at rest. It is highly desirable for the shaded areas 21 and 23 to be equal, in other words for the volume held by each ring 13 at rest to be sufiicient for the corresponding portion of the liquid charge.

In the second embodiment illustrated in FIGURE 2, the series of cells are formed by a stack of ring members 24 each furnishing a portion of cylindrical wall, shown at 25, and a portion of inwardly and upwardly inclined wall, shown at 26. The two wall portions join at the upper edge of the ring member 24 and this may take the form of a step or shoulder 27; a corresponding step or shoulder 28 is then provided on the lower edge of each ring member 24 and the assembly is built up by mating the shoulders 27 and 28 together and, if necessary, completing the resultant sealed joint by the use of a suitable sealant, adhesive or jointing compound. FIGURE 2 also illustrates the use of inclined lower cell rings, as opposed to the rimmed horizontal members shown in FIGURE 1. The areas 21, 22 and 23 occupied by the layers during operation and at rest are also shown.

The form of transfer assembly shown in FIGURE 1 is merely illustrative of the kinds which can be used and which are described in greater detail in application Ser. No. 495,610 of even date herewith, now abandoned, giving the advantage of gravity drainage during transfer.

I claim:

1. A liquid-liquid extraction apparatus for use in carrying out extraction using two mutually immiscible liquids,

which comprises a vertical column having a plurality of annular extraction cells and being adapted for rotation about a vertical axis, means for introducing the heavier of two mutually immiscible liquids into said cells, means for introducing the lighter of said liquids into one of the cells, means for introducing a material to be extracted into one of the cells, means for rotating said vertical column having said plurality of cells about the vertical axis in order to efiect centrifugal distribution of the two immiscible liquids, in the form of outer and inner layers in each of the cells, sump means on the lower side of each cell for retaining in such cell the contents of the cell when the apparatus is at rest without material on one cell entering and intermixing with material in another cell, and a plurality of vertically spaced scoop means equal in number to the cells mounted for collective rotation about a common vertical axis offset from the vertical axis of said column, said scoop means being adapted on collective rotation about said common axis to enter an associated cell by movement of such scoop means in a substantially horizontal plane whereby one end of each of said scoop means enters the inner of the two centrifugally distributed layers of liquid for transferring it to the next adjacent cell without transferring the outer of the two centrifugally distributed layers of liquid, said scoop means being adapted on further collective rotation about said common axis to be References Cited UNITED STATES PATENTS 1,353,463 9/1920 Dyer 23269 2,036,924 4/1936 Coutor 23269 X 2,734,635 2/ 1956 Holzenthal 23269 X 2,894,879 7/1959 Hickman l5918 3,111,393 11/1963 Cavanagh 23169 FOREIGN PATENTS 253,222 12/ 1960 Australia.

NORMAN YUDKOFF, Primary Examiner S. J. EMERY, Assistant Examiner US. Cl. X.R. 

